EP0718257A1 - Method of continuous fabrication of silicone-bonded pyrotechnic charges and composition for use in such a fabrication method - Google Patents

Abstract

In continuous mfr., by kneading and extrusion, of a pyrotechnical charge comprising mainly a cross-linkable silicone binder and an oxidant consisting mainly of (NH4)ClO4 or NaNO3, and charging the mixt. continuously into a press equipped at the outlet with an extrusion head, the uncross-linked binder contains: (i) a silicone resin with mol. wt. below 20,000, cross-linkable by hydrogen-silane gps.; (ii) a silicone gum with a mol. wt. above 100,000, cross-linkable by hydrogeno-silane gps.; and (iii) a hydrogeno-polysiloxane as cross-linking agent. A uniform paste is obtd. by extrusion at not above 30 degrees C, in the form of threads of stable geometry, which are cut to the length of the charge and cross-linked at above 30 degrees C.

Description

The present invention relates to the technical field of the pyrotechnic generation of gases which can be used in particular in systems for protecting the occupants of a motor vehicle by means of cushions which are inflated by the combustion gases of a pyrotechnic charge. More specifically, the invention relates to a process for the continuous manufacture of extruded composite pyrotechnic charges with silicone binder for pyrotechnic generators of clean and non-toxic gases. The invention also relates to composite pyrotechnic compositions generating gas with a silicone binder capable of being implemented using the process according to the invention.

For various pyrotechnic needs and in particular to ensure correct inflation of the protective cushions, pyrotechnic gas generators must supply in extremely short times, of the order of thirty milliseconds, clean gases, that is to say free of particles. solids liable to constitute hot spots which can damage the wall of the cushion, and non-toxic, that is to say low contents of nitrogen oxides, carbon oxides and chlorinated products.

Various families of pyrotechnic compositions have been developed for this purpose.

A first family relates to compositions based on alkali or alkaline earth azide in the presence of a mineral oxidant such as potassium nitrate or a metal oxide. These compositions, which can optionally include a binder, have two major drawbacks. On the one hand they produce during their combustion a lot of dust which must be filtered by filtration systems relatively which increases both the weight and the price of the generator. On the other hand azides are products very sensitive to humidity and these compositions are difficult to keep in good conditions for several years in a motor vehicle.

A second family relates to compositions based on nitrocellulose and nitroglycerin. These compositions, also known under the name of "double base powders", are very interesting because they burn very quickly and without producing dust. However, they have the disadvantage of not being completely stable over time due to the phenomenon of migration of nitroglycerin, a phenomenon which, over the years, affects the effectiveness of these compositions in a motor vehicle.

A third family relates to the so-called "composite" compositions basically consisting of an organic binder and an oxidizing mineral filler such as in particular a mineral perchlorate. These compositions are a priori very interesting because they have a good combustion speed and excellent aging stability.

It has thus been proposed by patent FR-A-2,137,619 or by its correspondent US-A-3,723,205 compositions whose binder is polyvinyl chloride and whose oxidizing charge is ammonium perchlorate in the presence of nitrate of sodium as internal chlorine sensor. However, the use of a chlorinated binder in the presence of energy charges is difficult to implement, in particular in terms of safety.

Composite compositions have therefore been proposed consisting of a silicone binder which can be crosslinked at room temperature, also known as a "Room Temperature Vulcanizable" binder, and potassium perchlorate, the potassium atom playing the role of internal chlorine sensor. Such compositions are, for example, described in patents FR-A-2 190 776 and FR-B-2 213 254 or in their American correspondents US-A-3,986,908 and US-A-3,964,256.

More recently, it has also been proposed in patent application WO94 / 06735 of composite compositions constituted by a silicone binder of the RTV type and by fillers of the metal azide or nitro compound type such as tetrazole.

The use of composite compositions with a silicone binder is indeed very advantageous in the field of motor vehicle safety insofar as the silicone matrix, during combustion, produces a vitreous residue which ensures a first filtration of the combustion gases. However, this type of composition has the drawback of being tricky to use if it is desired to use continuous manufacturing processes using an extrusion phase due to the poor mechanical strength of the non-crosslinked silicone binders. .

It is known from the teaching of patent US-A-3,367,816 to continuously extrude a paste of non-crosslinked silicone resin to ensure the internal coating of tubes manufactured continuously. But it is not known at the present time, to continuously extrude objects with non-crosslinked silicone matrix having a shape and dimensions perfectly defined and stable so that they can be cross-linked later without variation of the geometric parameters.

Pyrotechnic compositions with a silicone binder are therefore, at present, used in the form of granules and not in the form of a monoblock charge having a perfectly defined shape and dimensions because such charges cannot be obtained by continuous processes. , but only by discontinuous processes of shaping and baking in a mold which are prohibitively expensive for the automotive industry.

However, to ensure the operating reliability of the pyrotechnic generator subjected to numerous mechanical stresses, it is clearly preferable for the latter to contain a charge of pyrotechnic composition in the form of a block whose geometry is not very sensitive to mechanical stresses and in particular to repeated vibrations, rather than a bulk load of pellets.

A person skilled in the art is therefore looking for a continuous process which allows him to obtain composite pyrotechnic charges with silicone binder having a defined and reliable geometry, in particular in the case where said charge must have small thicknesses to be burned. .

The object of the present invention is precisely to propose such a process as well as composite pyrotechnic compositions with silicone binder which can be implemented by this process.

• i) une résine silicone de masse moléculaire inférieure à 20 000 et réticulable par des groupes hydrogéno-silanes,
• ii) une gomme silicone de masse moléculaire supérieure à 100 000 et réticulable par des groupes hydrogéno-silanes,
• iii) un réticulant qui est un hydrogéno-polysiloxane,

de manière à permettre la formation d'une pâte homogène qui est profilée par extrusion à une température au plus égale à 30°C sous forme de joncs à géométrie stable, les dits joncs ainsi obtenus étant alors découpés à la longueur du chargement et réticulés à une température supérieure à 30°C.The invention therefore relates to a process for the continuous manufacture, by kneading and extrusion, of pyrotechnic charges consisting mainly of a crosslinkable silicone binder, by an oxidizing charge essentially comprising ammonium perchlorate and sodium nitrate, and by additives, the said constituents of the load being introduced continuously into a extruder fitted at the outlet of an extrusion head, the said method being characterized in that the constituents of the said binder are introduced in non-crosslinked form and comprise at least:

• i) a silicone resin with a molecular mass of less than 20,000 and crosslinkable with hydrogen silane groups,
• ii) a silicone gum with a molecular mass greater than 100,000 and crosslinkable with hydrogen silane groups,
• iii) a crosslinker which is a hydrogen polysiloxane,

so as to allow the formation of a homogeneous paste which is shaped by extrusion at a temperature at most equal to 30 ° C. in the form of rods with stable geometry, the said rods thus obtained being then cut to the length of the load and crosslinked to a temperature above 30 ° C.

In general, the crosslinking temperature will be between 80 ° C and 120 ° C. It is thus possible, thanks to the use in the constituents of the binder of a gum and a resin of very different molecular masses, to obtain, in a single extrusion, rods with perfectly stable geometric ribs before and during crosslinking.

However, according to a preferred embodiment of the invention, the profiled rods are obtained after a double extrusion. According to this preferred embodiment, the homogeneous dough is extruded, at the outlet of the extruder, in the form of cords which are cut into strands and taken up in a shaping apparatus to be profiled by extrusion in the form of rods with stable geometry.

According to a first preferred variant of the invention, the shaping apparatus is a press equipped with an extrusion die.

According to a second preferred variant of the invention, the shaping apparatus is a extruder fitted with an extrusion head.

• a) d'abord un mélange constitué par la gomme et la résine,
• b) ensuite un mélange constitué par les charges oxydantes et les additifs,
• c) enfin l'agent réticulant.

According to a third preferred variant of the invention, the constituents of the load are introduced into the extruder in the following order:

• a) firstly a mixture consisting of gum and resin,
• b) then a mixture consisting of the oxidizing charges and the additives,
• c) finally the crosslinking agent.

• a) d'au moins une résine silicone de masse moléculaire inférieure à 20 000 et réticuble par des groupes hydrogéno-silanes Si-H, en mélange avec au moins une gomme silicone de masse moléculaire supérieure à 100 000 et réticulable par des groupes hydrogéno-silanes,
• b) avec au moins un réticulant qui est un hydrogéno-polysiloxane.

The invention also relates to compositions for pyrotechnic charge generating gas, capable of being implemented by the method. continuous according to the invention and constituted by a silicone binder, by an oxidizing charge essentially comprising ammonium perchlorate and sodium nitrate, and by additives, the said compositions being characterized in that the said binder is the product of reaction:

• a) at least one silicone resin of molecular mass less than 20,000 and crosslinkable by hydrogen silane groups Si-H, in mixture with at least one silicone gum of molecular mass greater than 100,000 and crosslinkable by hydrogenated groups silanes,
• b) with at least one crosslinker which is a hydrogen polysiloxane.

According to a preferred variant of the invention, the composition contains only one crosslinking agent which is reactive, both with respect to the resin and with respect to the gum.

Preferably, the resin is chosen from the group consisting of poly methyl, vinyl siloxanes and in particular poly vinyl dimethyl siloxane with a molecular mass of less than 20,000.

Preferably, the gum is chosen from the group consisting of poly methyl, vinyl siloxanes and in particular poly vinyl dimethyl siloxanes of molecular mass greater than 100,000 and poly methyl polyphenyl siloxanes of molecular mass greater than 100,000.

Preferably also, the crosslinker is chosen from the group consisting of polyhydrogenosilanes of molecular mass between 250 and 700.

According to another preferred variant of the invention, the molar ratio between said resin and said gum is between 9 and 2.

Among the additives may be a thickening agent which will moreover be advantageously chosen from the group consisting of silica, polytetrafluoroethylene and carbon black.

In some cases the thickening agent may be mixed with the crosslinking agent.

The fundamental originality of the invention lies in the fact that the silicone binder initially comprises, in addition to the crosslinking agent, on the one hand a crosslinkable silicone resin and on the other hand a crosslinkable silicone gum.

It is thus possible to adjust the viscosity of the non-crosslinked binder to a value such that by incorporating the oxidizing charge and the additives a paste is obtained which can be extruded and cut with stable geometric dimensions at a temperature below 30 ° C. .

When the load is placed in an oven, the crosslinking reactions of the resin and of the gum are completed, the crosslinking of the resin being faster than that of the gum. At the start of cooking, the gum is slow to soften, which mainly ensures the mechanical strength of the load and during cooking, when the non-crosslinked gum has softened and begins its crosslinking, it is the resin and the gum already crosslinked that provide the mechanical strength of the load.

The profiled rods can thus be cut to the desired length for loading and the structure of the binder is permanently fixed by crosslinking in an oven at a temperature between 80 ° C and 120 ° C, without geometric alteration.

Thanks to the compositions according to the invention it is thus possible to continuously manufacture extruded pyrotechnic charges with silicone binder whose shape and dimensions are perfectly reproducible without any machining after extrusion.

We now give a detailed description of the preferred embodiment of the invention with reference to Figure 1 which shows, in diagram form, an installation for implementing the method according to the invention, the arrows indicating the direction d advancement of products during the process.

In a twin-screw extruder 1 fitted at the outlet with an extrusion head 2 comprising several spinning outlets, the constituents of the charge are introduced, the constituents of the binder being introduced in non-crosslinked form. Such a extruder is also called a twin-screw extruder mixer.

As indicated in FIG. 1, preferably, the constituents are introduced in the following order.

First, at the head of the extruder, a mixture A is introduced consisting of the gum and the resin. Then a mixture B is introduced consisting of the oxidizing charges and the additives. Finally, the crosslinking agent C is introduced, optionally mixed with the thickening agent.

Said silicone resin has a molecular mass of less than 20,000, preferably between 1,000 and 3,000 and is crosslinkable by hydrogen silane groups -〉 Si-H. Preferably, said silicone resin will carry vinyl groups and will be chosen from vinyl polydimethylsiloxanes. Its functionality in vinyl groups will preferably be between 0.5 and 15 equivalents / kg.

Said silicone gum has a molecular mass by weight greater than 100,000, which can range up to a few million. Preferably, its molecular mass is close to 500,000 and it has a viscosity much higher than that of the resin, hence its name of gum.

It can be crosslinked by hydrogen silane groups. Preferably, said silicone gum will carry vinyl groups and will be chosen from vinyl polydimethyl siloxanes, or vinyl polymethyl polyphenyl siloxanes. Its functionality in vinyl groups will preferably be between 10 ^-4 and 5. 10 ^-3 equivalents / kg.

Preferably, the molar ratio between said resin and said gum will be between 9 and 2.

If the value of this ratio is greater than 9, the mixture does not contain enough gum to ensure stability of the geometric dimensions after extrusion; if the value of this ratio is less than 2, the mixture contains too much gum to be able to be injected by continuous pumping into the extruder.

When the mixture A consisting of the resin and the gum is introduced by means of a metering pump into the extruder, then the mixture B consisting of the oxidizing charges and the additives is introduced.

As an oxidizing charge, a mineral perchlorate and in particular ammonium perchlorate will advantageously be used. According to a particularly advantageous embodiment of the invention, a mixture of two types of ammonium perchlorate with different particle sizes will be used, so that the average particle size of the ammonium perchlorate is between 250 μm and 40 µm (micrometers or microns).

Since ammonium perchlorate produces chlorinated derivatives by combustion, it is necessary, for the purposes of automotive safety requirements, to add a chlorine sensor to it. The preferred chlorine sensor in the context of the present invention is sodium nitrate which fixes the chlorine in the form of sodium chloride of submicron size, therefore without risk of damaging the walls of the airbag.

The ammonium perchlorate / sodium nitrate weight ratio will advantageously be between 0.95 and 1.30.

The weight of the ammonium perchlorate + sodium nitrate mixture will advantageously be between 78% and 82% of the total weight of the composition.

Besides sodium nitrate, the composition can contain other additives as required, for example adhesion agents such as vinyl tri (2-methoxy-ethoxy) silane. However, when a thickening agent is used, the latter will advantageously be added in admixture with the crosslinking agent as explained below.

Finally, after introduction of the mixture B, the mixture C consisting of the crosslinking agent is introduced to finish with, where appropriate, the thickening agent.

Said crosslinking agent will be a hydrogen polysiloxane carrying hydrogen silane groups -〉 Si-H capable of reacting by polyaddition with the vinyl unsaturations of the resin and of the gum. Its molecular mass will advantageously be between 250 and 700. It will preferably be chosen from the group consisting of polymers of the polydimethyl siloxane type comprising hydrogen silane functional groups -〉 Si-H at a rate of 10 to 15 equivalents / kg and optionally vinyl functional groups at a rate of 1 to 5 equivalents / kg.

As indicated above, according to a preferred embodiment of the invention, the composition will contain only a single crosslinking agent, reactive both with respect to the resin and with respect to the gum.

The optional thickening agent may be chosen from the various thickening agents which can be used in silicone-bonded pastes, and will in particular be chosen from the group consisting of silica, polytetrafluoroethylene and carbon black. The mixture C is introduced into the extruder 1 by means of a metering pump.

The temperature of the constituents inside the extruder 1 is kept below 30 ° C.

The constituents of the composition are thus worked continuously in the twin-screw extruder 1 so as to form a homogeneous paste. It should be emphasized here that this dough has a very high viscosity and that the extruder 1 must be equipped with tools adapted to this kind of work.

The dough thus obtained is continuously extruded at the outlet of the extruder in the form of cords 3 which, thanks to the particular composition of the binder, have sufficient mechanical strength to be able to be cut into strands 5 in a cutting machine 4. The strands 5 are recovered by a conveyor belt 6 and routed in a shaping apparatus 7.

This apparatus 7 is basically an extrusion apparatus. It may be a press equipped with an extrusion die, but, preferably and as shown in FIG. 1, it will be a second extruder 7 equipped with an extrusion die 8.

The pyrotechnic composition thus undergoes a second extrusion during which it is profiled in the form of rods 9 with the desired geometry for the final pyrotechnic charge.

The rods 9 thus obtained are then cut, by a cutting tool 10, to the desired length for the pyrotechnic charge. The blocks 11 thus obtained are conveyed by a conveyor belt 12 to an oven 13 heated to a temperature between 80 ° C. and 120 ° C. so as to complete the crosslinking of the constituents of the binder and thus to freeze the structure of the blocks 11.

It is therefore thus possible, thanks to the invention, to manufacture continuously by extrusion, and without machining operations other than simple cutting, pyrotechnic charge blocks with silicone binder which are perfectly reproducible.

These blocks find their preferred application as pyrotechnic charges in gas generators intended to inflate a protective cushion for occupants of a motor vehicle. It has in fact been noted by the applicant that the joint presence, in the binder of the load, of a resin and of a gum as defined by the present invention, leads to combustion rates which are particularly well suited to the requirements of the automotive safety.

The examples which follow illustrate, without limitation, certain possibilities of implementing the invention.

Example 1

• mélange A :
  • résine : polydiméthyl vinyl siloxane (fonctionnalité : 0,95 éq/kg)
    de masse moléculaire : 1990
       70 parties en poids,
  • gomme : polydiméthyl vinyl siloxane (fonctionnalité : 4.10^-3 éq/kg)
    de masse moléculaire : 500 000
       30 parties en poids.
• mélange B :
  • perchlorate d'ammonium granulométrie 40 µm : 56,25 parties en poids
  • Nitrate de sodium : 43,75 parties en poids.
• mélange C :
  • réticulant : polyméthylhydrogénosiloxane : de masse moléculaire 400, fonctionnalité SiH : 13 éq/kg, fonctionnalité vinylique : 3 éq/kg.

According to the process represented in FIG. 1, hollow cylindrical blocks of pyrotechnic gas generator loading were made from the following mixtures of constituents (the abbreviation eq / kg representing equivalents / kg):

• mixture A :
  • resin: polydimethyl vinyl siloxane (functionality: 0.95 eq / kg)
    molecular weight: 1990
    70 parts by weight,
  • gum: polydimethyl vinyl siloxane (functionality: 4.10 ^-3 eq / kg)
    molecular weight: 500,000
    30 parts by weight.
• mixture B :
  • ammonium perchlorate particle size 40 µm: 56.25 parts by weight
  • Sodium nitrate: 43.75 parts by weight.
• mixture C :
  • crosslinking agent: polymethylhydrogensiloxane: of molecular mass 400, SiH functionality: 13 eq / kg, vinyl functionality: 3 eq / kg.

• mélange A : 18,2 parties en poids soit 10,92 kg/h
• mélange B : 80,0 parties en poids soit 48,00 kg/h
• mélange C : 1,8 parties en poids soit 1,08 kg/h.

We thus used:

• mixture A: 18.2 parts by weight, i.e. 10.92 kg / h
• mixture B: 80.0 parts by weight, i.e. 48.00 kg / h
• mixture C: 1.8 parts by weight, ie 1.08 kg / h.

The composition was extruded and cut into strands 5 which were extruded into hollow cylindrical rods 9 with an outside diameter of 39.8 mm and an inside diameter of 14.6 mm in a extruder.

The rods were cut into cylindrical blocks.

The blocks were baked in an oven at 120 ° C for 30 minutes.

After cooking, a dimensional variation of less than 0.2% is observed.

• . teneur en CO : 4 500 ppm
• . teneur en oxydes d'azote : 4 000 ppm
• . teneur en dérivés chlorés : inférieure à 10 ppm.

The combustion gas characteristics of these blocks necessary to inflate a 60 liter volume bag are as follows:

• . CO content: 4,500 ppm
• . nitrogen oxide content: 4,000 ppm
• . content of chlorinated derivatives: less than 10 ppm.

The combustion speed was 70mm / s at 20 MPa.

Example 2

• Mélange A
  • résine : polydiméthyl vinyl siloxane (de masse moléculaire 3 000 et de fonctionnalité en groupes vinyliques : 0,66 éq/kg) :
       80 parties en poids,
  • gomme : polydiméthyl vinyl siloxane (de masse moléculaire 500 000 et de fonctionnalité en groupes vinyliques : 4.10^-3 éq/kg) :
       20 parties en poids.
• Mélange B
  • analogue à l'exemple 1
• Mélange C
  • Polydiméthyl siloxane-vinyl-hydrogéno silane de masse moléculaire 350 et de fonctionnalités :
    • en groupe Si-H : 12 éq/kg,
    • en groupe vinyliques : 2 éq/kg.
    On a ainsi utilisé :
    • mélange A : 18,2 parties en poids soit 9,1 kg/h
    • mélange B : 80,0 parties en poids soit 40,0 kg/h
    • mélange C : 1,8 parties en poids soit 0,9 kg/h

The procedure was analogous to that of Example 1.

• Mix A
  • resin: polydimethyl vinyl siloxane (with a molecular weight of 3,000 and functionality in vinyl groups: 0.66 eq / kg):
    80 parts by weight,
  • gum: polydimethyl vinyl siloxane (with a molecular mass of 500,000 and functionality in vinyl groups: 4.10 ^-3 eq / kg):
    20 parts by weight.
• Mix B
  • analogous to Example 1
• Mix C
  • Polydimethyl siloxane-vinyl-hydrogen silane with molecular weight 350 and functionalities:
    • in Si-H group: 12 eq / kg,
    • in vinyl groups: 2 eq / kg.
    We thus used:
    • mixture A: 18.2 parts by weight, ie 9.1 kg / h
    • mixture B: 80.0 parts by weight, i.e. 40.0 kg / h
    • mixture C: 1.8 parts by weight, ie 0.9 kg / h

• teneur en CO : 4 000 ppm
• teneur en oxydes d'azote : 4 000 ppm
• teneur en dérivés chlorés : inférieure à 10 ppm.

Objects similar to those of Example 1 were manufactured which had a combustion speed of 55 mm / s at 20 MPa and whose combustion gases have the following characteristics for a volume of 60 liters:

• CO content: 4,000 ppm
• nitrogen oxide content: 4,000 ppm
• content of chlorinated derivatives: less than 10 ppm.

Example 3

• Mélange A
  • résine : polydiméthyl vinyl siloxane (de masse moléculaire 3 000 et de fonctionnalité en groupes vinyliques : 0,66 éq/kg) :
       65 parties en poids,
  • gomme : poly méthyl-vinyl poly phényl-vinyl siloxane (de masse moléculaire 2x10⁶ et de fonctionnalité en groupes vinyliques 10^-4 éq/kg) :
       35 parties en poids.
• Mélange B
  • perchlorate d'ammonium : (80 µm/200 µm : 50/50)
       43,64 parties en poids,
  • nitrate de sodium : 36,36 parties en poids,
• Mélange C
  Polydiméthyl siloxane vinyl hydrogéno silane de masse moléculaire 350 et de fonctionnalités :
  • en groupes silanes Si-H : 12 éq/kg,
  • en groupe vinyliques : 2 éq/kg.
     On a ainsi utilisé :
  • mélange A : 18,2 parties en poids soit 11,83 kg/h
  • mélange B : 80,0 parties en poids soit 52,00 kg/h
  • mélange C : 1,8 parties en poids soit 1,17 kg/h.
  On a fabriqué des objets analogues à ceux de l'exemple 1 qui présentaient une vitesse de combustion de 65 mm/s sous 20 MPa et dont les gaz de combustion présentent les caractéristiques suivantes pour un volume de 60 litres :
  • teneur en CO : 4 500 ppm
  • teneur en oxydes d'azote : 3 000 ppm
  • teneur en dérivés chlorés : inférieure à 10 ppm.

The procedure was analogous to that of Example 1.

• Mix A
  • resin: polydimethyl vinyl siloxane (with a molecular weight of 3,000 and functionality in vinyl groups: 0.66 eq / kg):
    65 parts by weight,
  • gum: poly methyl-vinyl poly phenyl-vinyl siloxane (of molecular mass 2x10 ⁶ and of functionality in vinyl groups 10 ^-4 eq / kg):
    35 parts by weight.
• Mix B
  • ammonium perchlorate: (80 µm / 200 µm: 50/50)
    43.64 parts by weight,
  • sodium nitrate: 36.36 parts by weight,
• Mix C
  Polydimethyl siloxane vinyl hydrogen silane with molecular weight 350 and features:
  • in Si-H silane groups: 12 eq / kg,
  • in vinyl groups: 2 eq / kg.
  We thus used:
  • mixture A: 18.2 parts by weight, i.e. 11.83 kg / h
  • mixture B: 80.0 parts by weight, i.e. 52.00 kg / h
  • mixture C: 1.8 parts by weight, ie 1.17 kg / h.
  Objects similar to those of Example 1 were manufactured which had a combustion speed of 65 mm / s at 20 MPa and whose combustion gases have the following characteristics for a volume of 60 liters:
  • CO content: 4,500 ppm
  • nitrogen oxide content: 3000 ppm
  • content of chlorinated derivatives: less than 10 ppm.

Claims (10)

Process for the continuous production, by kneading and extrusion, of pyrotechnic charges constituted mainly by a crosslinkable silicone binder, by an oxidizing charge essentially comprising ammonium perchlorate and sodium nitrate, and by additives, the said constituents of the charge being introduced continuously into a extruder (1) equipped at the outlet with an extrusion head (2), characterized in that the constituents of said binder are introduced in non-crosslinked form and comprise at least: i) a silicone resin with a molecular mass of less than 20,000 and crosslinkable with hydrogen silane groups, ii) a silicone gum with a molecular mass greater than 100,000 and crosslinkable with hydrogen silane groups, iii) a crosslinker which is a hydrogen poly siloxane, so as to allow the formation of a homogeneous paste which is shaped by extrusion at a temperature at most equal to 30 ° C. in the form of rods with stable geometry, the said rods thus obtained being then cut to the length of the load and crosslinked to a temperature above 30 ° C. Process for the continuous production of pyrotechnic charges according to Claim 1, characterized in that, at the outlet of the extruder (1), the homogeneous dough is extruded in the form of cords (3) which are cut into strands (5) and taken up in a switchgear shaping (7) to be profiled by extrusion in the form of rods (9) with stable geometry. Process according to Claim 2, characterized in that the shaping apparatus is a press equipped with an extrusion die. Method according to Claim 2, characterized in that the shaping apparatus is a extruder (7) equipped with an extrusion head (8). Method according to claim 1, characterized in that the constituents of the charge are introduced into the extruder in the following order: a) firstly a mixture (A) consisting of the gum and the resin, b) then a mixture (B) consisting of the oxidizing charges and the additives, c) finally the crosslinking agent (C) . Composition for gas-generating pyrotechnic charge, capable of being implemented by the method according to any one of claims 1 to 5 and constituted by a silicone binder, by an oxidizing charge essentially comprising ammonium perchlorate and nitrate of sodium, and by additives, characterized in that the said binder is the reaction product: a) at least one silicone resin of molecular mass less than 20,000 and crosslinkable by hydrogen silane groups in mixture with at least one silicone gum of molecular mass greater than 100,000 and crosslinkable by hydrogen silane groups, b) with at least one crosslinker which is a hydrogen polysiloxane. Composition according to Claim 6, characterized in that the said resin is chosen from the group consisting of vinyl polydimethylsiloxanes. Composition according to Claim 6, characterized in that the said gum is chosen from the group consisting of vinyl polydimethylsiloxanes and vinyl polymethyl polyphenyl siloxanes. Composition according to Claim 6, characterized in that the said crosslinking agent is chosen from the group consisting of polyhydrogenosilanes with a molecular mass of between 250 and 700. Composition according to Claim 6, characterized in that the molar ratio between the said resin and the said gum is between 9 and 2.

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